The present invention relates generally to a reverse osmosis systems for desalinization of water, and more specifically, to an interstage pressure boosting system of a multiple stage reverse osmosis system.
Reverse osmosis (RO) is a process widely used for desalinization of water. Reverse osmosis membranes are contained in a process chamber into which pressurized feedwater is admitted. A portion of the pressurized water permeates across the membrane and exits the process chamber as purified water at a low pressure and is referred to as permeate. The remainder of the water, still at high pressure, exits the process chamber and is referred to as a concentrate.
During the life of a membrane the fluid pressure must be adjusted slightly to ensure optimum operation. Without such optimization, the system will needlessly use energy or not produce the desired amount of permeate.
The concentrate from reverse osmosis systems may be used in three ways. The first way is to dispose of the concentrate by throttling the pressure with an orifice plate. The second way in which the high pressure concentrate may be used is to drive an energy recovery turbine (ERT). The output of the turbine is used to drive the feedwater into the system. The use of a turbine reduces the net energy consumption of the system. A third way in which to use the high pressure concentrate is to increase the pressure of the high level concentrate and admit the concentrate to a second reverse osmosis chamber to extract additional permeate. The high pressure concentrate from the second reverse osmosis chamber may then be handled in the above-mentioned three manners.
Referring now to FIG. 1, a known reverse osmosis system 10 is illustrated having a feed pump 12 which is driven by a motor 14 to pressurize feed fluid from a feed input 16. Pressurized fluid leaves pump 12 through an output 18 and enters a first reverse osmosis process chamber 20. The process chamber 20 has a permeate header 22 through which permeate is removed from the reverse osmosis chamber 20. Reverse osmosis chamber 20 also has a concentrate output 24 which removes concentrate from the reverse osmosis chamber 20 at a high pressure. The concentrate output 24 is coupled to a booster pump 26 which is driven by a booster pump motor 28. The booster pump 26 with booster pump motor 28 boosts the pressure of the concentrate before it is admitted into a second reverse osmosis chamber 30. The reverse osmosis chamber 30 has a permeate output 32 coupled to permeate header 22. A concentrate output 34 is coupled to an energy recovery turbine 36 which is coupled to a shaft 38 common to both motor 14 and pump 12. In this manner, some of the load of pump 12 is relieved by energy recovery turbine 36.
Another known arrangement similar to FIG. 1 is illustrated having the same components illustrated with the same reference numerals. In this embodiment, second energy recovery turbine 40 is coupled to concentrate output 34 is used to drive booster pump 26 on a common shaft 42. The energy recovery turbine 36 is thus used to recover any remaining energy in the concentrate.
One problem in known systems is that energy-wasting throttle valves and bypass lines are typically used to control the flow and the pressure of fluids to and from the reverse osmosis chambers. It would therefore be desirable to provide a reverse osmosis system that allows independent control of the flow and pressure of each reverse osmosis chamber without the use of energy wasting throttle valves and bypass lines.
It is therefore one object of the invention to provide a reverse osmosis system that may easily and energy-efficiently be adjusted to operate at its design capacity despite changes in the membrane characteristics due to fouling or other operating parameters.
In one aspect of the invention, a common shaft is used to rotatably hold a first pump fluidically coupled to the first feed inlet, a pump motor, a first energy recovery turbine fluidically coupled to the first concentrate outlet, and a second energy recovery turbine fluidically coupled to the second concentrate outlet. A second pump may also be coupled to the first concentrate outlet to increase the pressure of the first concentrate prior to entering the second process chamber.
In a further aspect of the invention, the second pump may be rotatably coupled to a booster pump motor. In another aspect of the invention, the second pump may be coupled to a third energy recovery device that is fluidically coupled to the second concentrate outlet.
In a further aspect of the invention, a method for operating a reverse osmosis system comprises the steps of:
providing energy from a first reverse osmosis process chamber to boost the pressure of feed fluid to the first reverse osmosis process chamber;
providing energy from a second process chamber to boost the pressure of feed fluid to a first process chamber; and,
collecting permeate form the first process chamber and the second reverse osmosis process chamber.
One advantage of the present invention is that energy-wasting throttle valves and bypass lines have been eliminated from the reverse osmosis process. Another advantage of the invention is that more energy is recovered from the process lowering the overall cost of operating such a process.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.